In the past, in order to connect integrated circuits to their packages, a solder bumping process was utilized. In this process, a vacuum sputtering deposition process was used to deposit a wetting metal, such as nickel, on top of the conductor. The wetting metal is necessary to reduce the surface tension of the solder so it will bond to the conductor. After deposition of the nickel, a thin film of oxidation-preventing material, such as gold, was deposited to protect the nickel from being oxidized. When oxidized, the nickel would prevent bonding of the solder to the conductor. After depositing the wetting and oxidation-preventing metals, a photolithographically patterned and developed photoresist was deposited on top over the conductor areas. The exposed areas of the photoresist were then etched away leaving the wetting and oxidation-preventing metals only on the conductor. Besides being relatively complex, the solder bumping process is costly because of the need to use gold.
Similarly, a solder bumping process was used to connect completed integrated circuit packages onto printed circuit boards. Again, a vacuum sputtering process is used to deposit a thin film of nickel on top of the copper. A subsequent sputtering process again deposits gold on top of the nickel to protect the nickel from being oxidized. Again a photoresist is developed with a pattern which covers the conductor area. The non-conductor areas are etched away to the base circuit board. Since printed circuit boards are much larger, this process requires more gold and is extremely expensive.
Since the solder bumping process is complex, time consuming, and expensive, improvements have been long sought but have also long eluded those skilled in the art.
Another seemingly unrelated problem has been that printed circuit boards, themselves, require a number of steps in their manufacture. This means that mass production techniques are the most advantageous and thus printed circuit boards are made the same over large production runs. The concept of individualizing printed circuit boards is almost unimaginable with current processes.